Ivermectin has been shown in an open, in-hospital trial in South India to be effective in clearing microfilaremia in patients with bancroftian filariasis at dosages as low as 25-mcg/kg given once orally. A second, blinded, placebo-controlled trial of ivermectin and the currently used drug, diethylcarbamazine (DEC), has completed its treatment but not follow-up phase. Preliminary findings suggest that the efficacy of Ivermectin and DEC are equivalent and that the side reactions induced by ivermectin may be significantly less. These findings and ivermectin's single-oral- dose mode of administration make it an excellent candidate to replace DEC as the drug of choice for treating lymphatic filariasis. Because long-term follow-up studies employing bronchoalveolar lavage to evaluate patients with TPE treated conventionally with diethylcarbamazine (DEC) have shown that approximately 1/3 relapse or have persistent low-grade alveolitis leading to pulmonary fibrosis, a therapeutic trial of three regimens (conventional DEC, long-term DEC, or DEC + steroids) has been initiated in Madras. The study will require about three years to enroll the anticipated 75 study patients. Observations on 200 Peace Corps volunteers going to Loa loa endemic areas of Africa are concluding after three years of a placebo-controlled chemoprophylaxis trial using weekly doses of DEC. Seroconversion is at approximately 15% but final analysis of the results is not yet complete.